Currently, in a mobile telephone terminal and mobile network using the third generation W-CDMA technology, a voice telephony service is implemented as follows: A radio base station receives a signal from a mobile telephone and a radio network controller (RNC) collects these signals and connects them to a circuit switching equipment on a mobile circuit switched network using a circuit switched protocol.
With research and development of high-speed and large-capacity technology for mobile network, the future trend of mobile network is towards achieving higher speed and larger capacity based on the IP. At the present time, HSDPA (High Speed Downlink Packet Access), HSPA (High Speed Packet Access), EVDO Rev. A, and EVDO Rev. B have already been put to practical use.
In the near future, progress of high speed network will be achieved. The trend is that the LTE (Long Term Evolution), EPC (Evolved Packet Core), UMA (Ultra Mobile Access), Mobile WiMax (WiMax is a trademark of WiMax Forum), or the like aiming at 100 Mbps (Mega bits per second) or more in downlink direction and at 50 Mbps or more in uplink direction will be introduced.
Further, the future trend is that an access point such as a femtocell, Home NodeB, Home eNodeB, or the like will be installed in home and voice call traffic each in home and enterprise will be supported via a mobile high-speed network.
In case an access point is such as a femtocell, Home NodeB, Home eNodeBs, or the like, VoIP (Voice over IP) based voice communication is used between the access point and a terminal connected thereto.
Patent Document 1, found by the present applicant in a prior art document search on a gateway, discloses a heterogeneous network connection gateway that connects a first network and a second network using a signal format different from the first network and comprises a conversion unit which converts a signal used in the first network into a signal used in the second network and which converts the signal used in the second network into the signal used in the first network when a terminal connected to the first network and a terminal connected to the second network communicate with each other; a detector that detects conversion process information including at least one of the following information items: time needed for the conversion unit to convert a signal or an amount of data converted; and a network connection unit that is connected to at least one of the first network and the second network and that transmits the conversion process information to a billing system of the first network or the second network; and the conversion unit that converts at least one of a call processing signal by call connection signaling, an audio signal generated by an audio codec, and an image signal generated by an image codec.
Further, Patent Document 2 discloses a configuration of a multimedia information replay system, in which conversion control means holds an attribute conversion table indicating conversion process contents only when multimedia information received from a first multimedia communication terminal cannot be provided to a second multimedia communication terminal, unless (an attribute such as coding system, coding rate, and multiple parameters of) the multimedia information is converted, and video conversion means and audio conversion means convert video information and audio information included in the multimedia information received from the first multimedia communication terminal according to the conversion process contents indicated by the attribute conversion table and provides the converted information to the second multimedia communication terminal.
Further, as a gateway, Patent Document 3 discloses a configuration of a communication system (SYS) in which an IPv4 private network (IPv4), global IPv4 Internet (IN) and IPv6 network (GV6) are interconnected through a first (AGW) and second (BGW) gateway, “IPv6 in IPv4 tunnels” are set up through the IPv4 private network (PV4) and the global IPv4 Internet (IN) in order to allow communication from a first fixed terminal (A1) of the IPv4 private network (PV4) to a second fixed terminal (B) of the IPv6 network (GV6), mapping tables in the first (AGW) and second (BGW) gateway can be set up and are used in the communication between the first terminal (A1) and the second terminal (B) on the basis of a global IPv6 address assigned to the first dual-stack terminal (A1), the usage of tunnels in particular avoid the usage of a Virtual Private Network (VPN) for the communication initiated from the first terminal (A1) to the second terminal (B).
Further, regarding security management by a server and gateway, Patent Document 4 discloses a configuration of a system for dynamic filtering of a data packet at an access gateway in a communication network in which a policy server receives a request for registration with the network from a network node, the server verifies the network node identity and selects the corresponding security policy for the network node, the selected security policy is indicated by the server to a network access gateway; the network access gateway selects the indicated security policy, and the selected security policy is applied for the communication between the network node and the network.
None of Patent Documents 1 to 4 mentioned above discloses a configuration of a gateway that interconnects an access point such as a femtocell, HNB (Home NodeBs), HeNB (Home eNodeB) and so force to a second gateway apparatus that connects a mobile circuit switched network and an IMS network, and that realizes interconnection between voice communication on an access point, voice communication on the mobile circuit switched network, and voice communication on the IMS network. The inventions described in Patent Documents 1 to 4 are entirely different from the present invention described below.
[Patent Document 1]
    Japanese Patent Kokai Publication No. JP-P2004-222009A[Patent Document 2]    Japanese Patent Kokai Publication No. JP-P2005-072973A[Patent Document 3]    Japanese Patent Kohyo Publication No. JP-P2007-524257A[Patent Document 4]    Japanese Patent Kohyo Publication No. JP-P2008-512958A